Patient organisations are often characterised in sociological literature as patient representatives, speaking for people affected by an illness in medical, political and scientific spheres. Using Motor Neurone Disease and Parkinson’s organisations as case studies, I investigate the challenges faced by patient organisations attempting to fulfil this role, focusing in particular on the need to balance responsibilities associated with care and campaign functions and increasing engagement in research. The principal focus of this PhD is to examine different conceptualisations of representativeness that have been discussed overtly and implicitly by participants. I have examined the extent to which patient organisations represent their members’ needs and cultivate a sense of collective identity, the way in which the patient organisations represent their members during the setting of research agendas, and finally I have considered the extent to which representation coincides with the concept of patient involvement.